1. Field of the Invention
The present invention generally relates to an optical printing apparatus for exposing light onto a photosensitive recording medium to form a gradation image. More specifically, the present invention is directed to such an optical printing apparatus. That is, while one column, or plurality of columns constituted by switching elements (e.g., liquid crystal shutter elements) are arranged as a print head, the respective elements are independently controlled in response to image data so as to print out a gradation image in the optical printing apparatus.
2. Description of the Related Art
Various sorts of optical printing apparatuses have been developed as apparatuses employing instant films and simultaneous color paper, and are commercially available in the markets. In these optical printing apparatuses, light is exposed onto photosensitive recording media so as to form gradation images.
A conventional optical printing apparatus will now be explained with reference to a drawing. FIG. 19 is a perspective view for schematically indicating a structure of a conventional optical printing apparatus as disclosed in, for instance, Japanese Patent Application Laid-open No. 7-256928.
In FIG. 19, white light emitted from a halogen point light source 100 is separated into red-colored light, green-colored light, and blue-colored light by way of a color liquid crystal (LCD) shutter 101. The R, G, B-colored light is continuously irradiated onto an edge surface of an acrylic rod 9 in a time shift manner. In this print head, the acrylic rod 9 is covered with a reflection foil on which aluminum and the like are vapor-deposited except for a light emitting plane thereof. Thus, this acrylic rod 9 owns such a function capable of effectively converting light entered from a rod edge surface into line-shaped light. As a result, the red line-shaped light, the green line-shaped light, and the blue line-shaped light are continuously irradiated onto a black/white shutter array 10 in a time shift manner.
In this case, 3 columns of pixel arrays corresponding to the red light, the green light, and the blue light are provided inside the black/white shutter array 10. These pixel arrays are driven in such a manner that only designated color light can pass therethrough. For example, when the red line-shaped light is irradiated, this red line-shaped light can pass through only one pixel array corresponding to the color light, whereas the other two pixel arrays are kept under shield condition.
Then, the red line-shaped light, the green-shaped light, and the blue line-shaped light, which are modulated by the black/white shutter array 10 are focused on a photosensitive paper such as the spectra instant film manufactured by Polaroid Inc., by using a SELFOC lens array 12 (namely, tradename of converging lens array). At this time, since the photosensitive paper is relatively transported with respect to the black/white LCD shutter array 10, the red line-shaped light, the green line-shaped light, and the blue line-shaped light are sequentially exposed onto the same place on the photosensitive paper. As a result, a two-dimensional print image can be obtained.
In the above-described conventional optical printing apparatus, there is a problem in that the images having high image qualities cannot be formed under stable condition due to the variation and the exposure conditions, which are caused by differences in the response speeds of the light sources and/or the liquid crystal shutter elements (arrays), or differences in the drive conditions of these LCD shutter elements.
Concretely speaking, the transmittance of the LCD shutter element varies due to the basic characteristic thereof, i.e., the differences in the intervals of driving the LCD shutter elements. For instance, in an LCD shutter element corresponding to a recording pixel subsequent to a non-recording pixel, and also in LCD shutter elements corresponding to pixels where recording pixels are continued, the transmittance thereof is changed due to differences in histories thereof. Also, in the case that the LCD shutter array is constructed as a single column, and the red, green, and blue light sources are sequentially turned ON so as to construct the low-cost optical printing apparatus, color shift may occur because of the temporal shifts. Also, when these red, green, and blue light sources are sequentially switched, the light leakage phenomenon will occur. As a result, there is another problem that the correct image cannot be formed.
The present invention has been made to solve the above-explained problems, and therefore, has an object to provide an optical printing apparatus capable of recording an image having a high image quality, but without having any deterioration in quality and color shift. These deterioration of the image quality and color shift problems are caused by the difference in the intervals of driving LCD shutter elements.
To achieve the above-described object, an optical printing apparatus, according to a first aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, in which the print head contains a light source and a plurality of liquid crystal shutter elements, comprising: image data input means for inputting image data; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data input means with the reference level so as to convert the multi-value data into binary data; data transferring means for transferring the binary data outputted from the comparing means as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby the print head is driven in response to the output results of the data transferring means, the latch control means, and the strobe control means to thereby form the gradation image, and also the liquid crystal shutter element corresponding to a non-recording pixel is ON/OFF-driven.
Also, an optical printing apparatus, according to a second aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, in which the print head contains a light source and a plurality of liquid crystal shutter elements, comprising: image data input means for inputting image data; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data input means with the reference level so as to convert the multi-value data into binary data; a selector for selecting any one of the binary data outputted from the comparing means and binary data of xe2x80x9c1xe2x80x9d; data transferring means for transferring the binary data outputted from the selector as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby the print head is driven in response to the output results of the data transferring means, the latch control means, and the strobe control means to thereby form the gradation image, and also the liquid crystal shutter element is ON/OFF-driven for arbitrary time irrespective of the image data.
Also, an optical printing apparatus, according to a third aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, in which the print head contains a light source and a plurality of liquid crystal shutter elements, comprising: image data input means for inputting image data; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data input means with the reference level so as to convert the multi-value data into binary data; data transferring means for transferring the binary data outputted from the comparing means as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby after the light source was turned ON, a preselected time period has passed, and then the liquid crystal shutter element is ON/OFF-driven; and also the print head is driven in response to the output results of the data transferring means, the latch control means, and the strobe control means to thereby form the gradation image.
Also, an optical printing apparatus, according to a fourth aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, in which the print head contains a light source and a plurality of liquid crystal shutter elements, comprising: image data input means for inputting image data; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data input means with the reference level so as to convert the multi-value data into binary data; data transferring means for transferring the binary data outputted from the comparing means as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby the liquid crystal shutter element corresponding to a non-recording pixel is ON/OFF-driven, while the light source is not turned ON.
Also, an optical printing apparatus, according to a fifth aspect of the present invention, is featured by such an optical printing apparatus for selectively exposing light emitted from a print head onto a photosensitive recording medium to thereby form a gradation image, in which the print head contains a plurality of light sources and a plurality of liquid crystal shutter elements, comprising: image data input means for inputting image data; reference level producing means for producing a reference level; comparing means for comparing multi-value data outputted from the image data input means with the reference level so as to convert the multi-value data into binary data; data transferring means for transferring the binary data outputted from the comparing means as head data to the print head; latch control means for latching data of the print data; and strobe control means capable of causing the print head to expose the light therefrom; whereby the plurality of light sources are switched plural times larger than a total number of the light sources within 1 line.
An optical printing apparatus, according to a sixth aspect of the present invention, is featured by that a shape of the liquid crystal shutter element is formed in such a manner that a length of the liquid crystal shutter element along a sub-scanning direction is made shorter than that along a main scanning direction.
An optical printing apparatus, according to a seventh aspect of the present invention, is featured by that when the light sources are switched, the liquid crystal shutter elements are shielded.
An optical printing apparatus, according to an eighth aspect of the present invention, is featured by that the plurality of liquid crystal shutter elements are positive type liquid crystal elements.
Furthermore, an optical printing apparatus, according to a ninth aspect of the present invention, is featured by that the plurality of liquid crystal shutter elements are TN (twisted nematic) type liquid crystal elements.